Ludwig I've been impressed with the CG 125 cc (Hensim, a Taiwanese clone) I mounted in the Simplex, pretty much what you told me to expect. Weight is a modest 55 lbs not bad considering the wet clutch, kick start & 5 speed transmission. Hp 10 to 12... depends on which source you choose believe. It's plenty for a smooth running economical...120 mpg quoted for a two hundred twenty pound motorcycle & lightweight rider. After riding for several weeks I'm quite certain that estimate isn't too far fetched. Gear changes are smooth and positive...little beast even starts well. The two engines I purchased shipped in bare basic form so all electricals, fuel/carb system, exhaust, shift and kick levers must be acquired separately. No manuals with either engine, which will probably be a negative for a novice, but plenty of info on the net to get it properly wired, fueled and lubricated. I purchased a shop manual CD on ebay which gives more detail than most will probably require, but also has info on service intervals etc.
Mounting on the Simplex was a breeze once I freed up enough room in the frame. You need a big frame to mount these 17" H x 14" W x 13" L. I have a drop loop Flyer frame coming & I anticipate having to drop the loop some as well as alter the down tube to make room forward. Though I'm hoping I can fit without cutting. I'd like the motor to sit as low as possible in the frame to lower the center of gravity. Speculation at this point but UPS tracking puts delivery next Thursday & speculation at an end.
While I'd relish seeing a 3 wheeler with CG 5 speed installed, my limited knowledge of trikes renders my opinion on utilizing a CGxxx power source rather worthless in the matter. Rick C.